Analysis Of The Characteristics Of Drought In Northeast China And The Causes Of Typical Drought Process

Based on the daily precipitation and temperature data of 207 meteorological stations in Northeast China,four common meteorological drought indices in Northeast China are calculated and their applicability is comparatively analyzed.Index with the best applicability among these four indices is selected to analyze the drought phenomena and drought processes of different drought grades in Northeast China from 1961 to 2014.Finally,origin analysis is carried out to the selected typical drought year in the latest 54 a,using NCEP/NCAR monthly analysis data,in terms of the main atmospheric circulation characteristics of drought in Northeast China.This work includes comparison of the applicability of drought indices,drought characteristics analysis and origin analysis of the typical drought event.Main conclusions are as follows:1.In Northeast China,the temporal evolution of drought duration days and drought process intensity obtained by four meteorological drought indices is basically consistent.The SPI and SPIW indices have poor performance of the influenced area for longer drought processes.Compared with that,the MCI index can reflect the drought impact range of various time periods.In the spatial distribution,SPI and SPI indices have no obvious spatial meridional variations.MCI and MI indices are spatially consistent in that they all have a meridional distribution and decline from west to east.From the drought affected area at different time scale,the spatial distribution of the intensity of drought and drought duration and the index calculation method,MCI index is close to the actual disaster.2.Through the analysis of the seasonal characteristics of different drought grades and drought processes,spring is found to be the main occurrence period of drought event in Northeast China,while in summer there will be more serious drought.In recent 54 years,the interannual variation of accumulated intensity of the occurrence of drought in Northeast China is basically in accordance with the interannual variation of the affected area of drought.In terms of spatial distribution,the drought is more serious in Northeast Plain;while eastern Liaoning and southern Jilin are least affected by drought;the Xiao Hinggan Mountains and the San Jiang Plain in the northeast are light drought regions.Based on the REOF analysis of the drought process in Northeast China,it is found that the Northeast region can be divided into three regional modes: Liao river mode(mainly located in the Northeast Plain area),Da Hinggan Mountains central mode and San Jiang plain mode.3.During spring and summer time,in the middle layer(500hPa),the location of the Western Pacific subtropical high is easily anomaly southward and the intensity is relatively weaker than normal,the Northeast cold vortex is not active,and the location of the East Asian trough and the North American trough are easily anomaly eastward in dry years.In the lower layer,there is an obvious anti-cyclonic vortex exist to the south of Lake Baikal in spring.The northeastern part of China is mainly controlled by the easterly or northeasterly airflow,while in the summer time,the northwesterly air flow controls this area.Based on the analysis of the physical variables on each layer,we can conclude that in the most area of Northeastern China the low layer is divergent,while the high layer is convergent,and the vertical direction is controlled by abnormal sinking movement.From the perspective of water vapor transport,the confluent location of the water vapor belt from the Bay of Bengal and from the Sea of Japan is obviously anomaly southeastward in the Northeastern China,which leads to less water vapor transport in the Northeastern China in summer.What's more,the Northeastern China lies in the divergent area of water vapor,which is one of the important reasons for drought occurs frequently in the northeastern China in spring and summer.